The invention relates to a bath condenser with a condenser block that has evaporation passages for a liquid and liquefaction passages for a heating medium and at least two circulation sections that are located on top of one another, the evaporation passages each having on the lower end of a circulation section at least one entry opening for the liquid and on the upper end of a circulation section at least one exit opening, and there being means for routing liquid from an exit opening of one circulation section to an entry opening of the underlying circulation section.
In a low-temperature air separation system with a pressure column (commonly referred to as a high pressure column) and a low-pressure column, liquid oxygen from the low-pressure column is evaporated against gaseous nitrogen from the pressure column in indirect heat exchange in a heat exchanger, the nitrogen condensing.
The heat exchanger is implemented essentially in two different basic forms. In a falling-film evaporator, the liquid to be evaporated is delivered at the top to the evaporation passages via a distribution system that at the same time forms a gas seal. The liquid runs down as a liquid film over the heating surface, its being partially evaporated. The resulting gas and the unevaporated residual liquid emerge at the bottom from the falling-film evaporator. The liquid collects in the collecting space located under the condenser, while the gas portion is relayed on.
In a bath condenser, on the other hand, the condenser block is in the liquid bath from which liquid is to be evaporated. The liquid from underneath enters the evaporation passages of the condenser block and is partially evaporated against the heating medium that flows through the liquefaction passages. The density of the medium that is evaporating in the evaporation passages is less than the density of the surrounding liquid bath, resulting in a siphon action, so that liquid from the liquid bath flows into the evaporation passages. The greater the immersion depth of the condenser block in the liquid bath, the higher the average hydrostatic pressure becomes in the evaporation passages and the more poorly the liquid evaporates, since the boiling point of the liquid rises according to the vapor pressure curve.
The efficiency of a bath condenser can therefore be increased by dividing the condenser block into several sections that are located on top of one another, hereinafter called circulation sections. The advantage of one such arrangement is that the immersion depth for several circulation sections is smaller than for a single high condenser block. Thus, the hydrostatic pressure in the evaporation passages becomes less, and the liquid can evaporate more easily.
German patent application 199 39 294 discloses a multistory bath condenser in which there are two condenser blocks parallel to one another and in which between the blocks for each story there are liquid storage tanks for the liquid that is to be evaporated. The evaporation passages are divided vertically into several stories that each form its own circulation section, Thus the immersion depth is kept relatively small.
In the individual circulation sections, liquid flows from underneath into the evaporation passages and emerges again as a liquid-gas mixture on the top end of the circulation section on the side of the condenser block that is opposite the entry side. The emerging liquid is routed around the condenser block via lines and flows back again into the liquid storage tank. The complex piping and large space requirement that arise due to the two parallel condenser blocks and the necessary piping are disadvantageous in this arrangement.
The object of this invention is therefore to develop a compact multistory bath condenser.
This object is achieved by a bath condenser of the initially mentioned type, in which the means for routing the liquid connect only exit openings and entry openings that are located on the same side of the condenser block.
As claimed in the invention, the bath condenser consists of at least two circulation sections that are located on top of one another and that are each supplied with liquid from its own liquid storage tank. The vertical subdivision of the bath condenser can greatly reduce the liquid level in the liquid storage tanks of the respective circulation sections relative to the liquid level in the single continuous condenser block.
The liquid enters the evaporation passages via the entry openings that are located on the bottom end of a circulation section, flows upward, partially evaporates and leaves the passages on the top end of the circulation section via suitable exit openings. The liquid portion in the liquid-gas mixture emerging from the passages flows, on the one hand, back to the entry openings of this circulation section, and, on the other hand, depending on the liquid level in the liquid storage tank of the circulation section, to the entry openings of the underlying circulation section in order to be overturned there in turn via the evaporation passages.
The exit and entry openings between which liquid flows are all located on the same side of the condenser block in the bath condenser as claimed in the invention. Therefore, complex piping is not necessary to repeatedly overturn the liquid within a circulation section or to feed it to an adjacent circulation section.
Preferably at most two sides of the condenser block are provided with entry and/or exit openings. As claimed in the invention, however, the entry and exit openings that are located on different sides of the condenser block are not connected to one another on the liquid side outside of the condenser block, i.e., the liquid that emerges from an exit opening on one side of the condenser block cannot flow into an entry opening that is on the other side of the condenser block. Within the condenser block, however, fundamentally exchange of liquid between the evaporation passages to a small degree is possible, since the corrugated sheets that separate the individual evaporation passages from one anther are often perforated. If there are entry and exit openings on both sides of the condenser block, the condenser block has two parallel groups of evaporation passages between which no liquid is exchanged. The liquid emerging from the exit openings on one side is routed exclusively in the evaporation passages with entry openings that are likewise located on this side.
In an especially preferred embodiment, on the two opposing sides of the condenser block, there are entry and exit openings to the evaporation passages in each case. In this case, it is especially advantageous if the condenser block is built mirror-symmetrically to the center plane between these two sides.
A more compact execution of the bath condenser can be achieved by all entry and exit openings being located on the same side of the heat exchanger. Lines to connect the entry or exit openings to one another are only necessary on the outside of the condenser block. The other three lateral boundaries of the bath condenser are formed by the outside walls of the condenser block. If nothing else arises from this connection, the indications xe2x80x9ctopxe2x80x9d, xe2x80x9cbottomxe2x80x9d and xe2x80x9claterallyxe2x80x9d each relate to the alignment of the condenser that is present during operation of the bath condenser and in which the individual circulation sections are located essentially vertically on top of one another.
Preferably the flow connection between the entry or exit openings and the evaporation passages is produced by horizontally or obliquely running channels. The condenser block is built from several corrugated plates that are stacked on top of one another and that are each bordered by flat partitions. In this case, the plates and partitions form the liquefaction and evaporation passages. In the area of the entry or exit openings to the evaporation passages, the corrugated plates are arranged slanted so that fluid that flows into the evaporation passages that run vertically is deflected to the entry or exit openings that are located in a side wall of the condenser block.
The side of a circulation section in which the entry and/or exit openings are located is advantageously provided with a collector that has a liquid feed line and a gas offtake. A circulation section generally has rectangular side walls. The collector covers at least the entry and exit openings of the side wall of the circulation section, but preferably the entire side wall of the circulation section. The walls of the collector and the side wall of the circulation section therefore form a volume that is shielded against the environment and that is gastight and liquid-tight except for the feed lines and offtake that are intended for this purpose.
The bath condenser in this variant is bordered laterally by the side walls of the condenser block, or on the sides on which the entry and/or exit openings are located, by the outside walls of the collectors. A separate tank around the bath condenser is not necessary, by which the condenser becomes extremely compact. In this way, material for the tank wall is saved and the entire length of the welds necessary for production is greatly reduced, by which production is simplified. Moreover, smaller wall thicknesses can be selected for the collector than for the otherwise necessary tank wall, since the diameters of the collectors need not be made as large as that of the tank around the condenser block. This provides a considerable savings in costs.
It has been found to be especially advantageous to cover the sides of several circulation sections, especially the entire side of the condenser block in which the entry and/or exit openings are located, with a collector that is provided with a liquid feed line and a gas offtake. In this collector, for each circulation section there is a suitable liquid storage tank. Furthermore, in the collector or on the collector, there are lines or openings for delivery and discharge of liquid and/or gas into and out of the circulation section.
Preferably the collector on the boundary of two circulation sections is divided in each case into stages, two adjacent stages being connected to one another on the flow side via one liquid line and one gas line. The collector that extends over the height of several circulation sections, preferably over the entire height of the condenser block, is divided into stages according to the circulation sections. The stages are delineated against one another preferably by flat sheets or elbowed bottoms. It is especially favorable if the individual stages are delineated gas-tight and liquid-tight against one another except for flow connections that are intended especially for this purpose such that the volume of one stage can be used as the liquid storage tank for the bordering circulation section.
Liquid transport from one stage to the underlying stage is advantageously ensured via an overflow pipe. The bottom of one stage of the collector is penetrated by the overflow pipe with an opening located above the bottom. The liquid that flows into this stage from the circulation section collects on the bottom of the stage and drains into the underlying stage only when the liquid level has reached the height of the opening of the overflow pipe. At a lower liquid level, the liquid is overturned only in the upper of the two stages.
By dividing the collector into several stages, essentially only the gas that has been evaporated in the assigned circulation section flows through one stage. The gas velocities in one stage are therefore relatively low, especially much lower than in a bath condenser in which there is no separation of the collecting areas for the gas. In this way, the danger that the evaporated gas will entrain so much liquid that the liquid level drops to under the opening to the flow connection to the adjacent stage, for example to under the entry edge of the overflow pipe, is avoided.
The danger of the entrainment of liquid can advantageously be further reduced by the entry into the gas line of one stage being located above the exit opening of the evaporation passages of the stage. The gas that has evaporated in the circulation section must rise a certain distance before it enters the gas line by which it is discharged from the stage. The volume between the exit opening from the circulation section and the inlet into the gas line is used as an additional separation space in which the liquid that is entrained with the gas is separated from the gas flow.
It has proven especially favorable to provide the gas inlet of the gas line on the side that faces away from the exit opening of the evaporation passages. The gas that emerges from the exit opening is then deflected again in the stage before it enters the gas line, by which the liquid is more easily separated from the gas flow.
The construction effort for the collector can be kept low by the collector in a plane perpendicular to the liquefaction and evaporation passages having a semicircular or semielliptical cross-section, i.e., implemented, for example, by a sheet that has been bent into a semicircle and that is connected to the two edges of the condenser block side that is provided with the entry or exit openings.
The liquid or gas lines that connect two stages to one another or that discharge gas from one stage run preferably within the collector. Especially preferably both the liquid and also the gas line are housed within the collector. The bath condenser therefore remains extremely compact and is bordered to the outside only by the outside walls of the condenser block and the collectors. No lines run laterally outside of these boundaries over most of the body of the bath condenser. Only at least one feed line and one offtake at a time for the fluid to be evaporated and the fluid to be condensed are, of course, necessary. They preferably emerge on the top and bottom ends of the bath condenser.
Preferably there is one gas line that extends through all stages and that has one gas inlet in each stage.
The bath condenser as claimed in the invention can be advantageously used especially as the main condenser of a low-temperature air separation system.